This invention relates to processes for treating spent caustic effluents, for example, effluents from petroleum refineries, aluminum manufacturing, food processing or the like.
Many industrial operations generate dilute spent caustic effluents such as petroleum refining processes. A typical dilute spent caustic effluent from such refineries may contain about 5% to 12% sodium hydroxide (w/w) with varying but significant quantities of organic compounds that include a range of mercaptans, sulfidic oils, naphthenic acids, cresylic acids and derivatives. Included in the mixture are lesser quantities of other inorganic and organic compounds. In addition, a petroleum refinery effluent may contain approximately 5% to 20% by volume of oil along with the aqueous caustic solution. Traditionally such effluents have been considered essentially useless waste streams but have required significant processing before disposal to avoid contamination of the environment.
The patent to Helleur No. 4,079,585 describes a method and apparatus for removal and recovery of a constituent from industrial and municipal waste streams by evaporation and concentration of the constituent as a result of intimate and turbulent contact between the waste stream liquid and hot gases produced by combustion in a scrubbing tower and states that submerged combustion techniques can also be used to advantage in the process. According to that patent undesirable volatile pollutants can be removed without vaporizing them by addition of an alkali such as lime or caustic to retain acidic volatile pollutants such as sulfur dioxide, hydrogen sulfide, etc. in solution so that they can be disposed of in liquid form. The Helleur patent describes the process as being applicable to spent material from such industries as the oil industry and notes that, to avoid vaporization of selected combustible volatiles, the temperature of the combustion gases should be maintained below the flash point of the volatiles by cooling the combustion gas before contact with the liquid.
The Young et al. U.S. Pat. No. 4,16,028 discloses a submerged combustion evaporator as the first stage in a process for concentration of constituents of industrial waste streams.
In the Ohkawa et al. U.S. Pat. No. 3,966,594, treatment of waste water containing water-soluble organic substances in various ways is described and the submerged combustion method is stated to be industrially insufficient in terms of concentration and combustion. Instead, that patent describes a process in which the waste water is treated with a water-insoluble organic solvent solution of an organic constituent.
According to the Anderson U.S. Pat. No. 4,188,291 industrial waste water is processed by a submerged combustion evaporator and carbon dioxide in the combustion gases supplied to the waste water is sequestered by calcium hydroxide which has been added to produce calcium carbonate which is then separated from the waste stream.
The spent caustic treatment process described in the DeRoeck et al. U.S. Pat. No. 5,244,576 introduces refinery gases containing carbon dioxide and hydrogen sulfide into a sodium hydroxide solution to convert the carbon dioxide to sodium carbonate.
In the Connally U.S. Pat. No. 3,985,609 concentration of constituents in a liquid to be concentrated is effected by supplying the liquid to a submerged combustion evaporator.
The Echols U.S. Pat. No. 5,934,207 describes evaporation of leachate by directing flames from a burner to which landfill gas is supplied into a fire tube heater immersed in a tank containing leachate so as to heat and vaporize the liquid constituents in the leachate while disposing of the landfill gas.
The Duesel U.S. Pat. No. 5,342,482 discloses the use of landfill gas as a fuel source for a submerged combustion gas evaporator in a leachate evaporation process.